Dull burning pain around navel, under breastbone and sometimes moves lower right side. never seems to go away. could i have an ulcer or appendicitis?

Unlikely: At your age ulcers, while possible, are very rare and not likely to move about or be dull. Appendicitis is an acute inflammatory condition that would involve fever and often gives only a few hours before bursting and you'd be at the ER. Sounds like gastric response to combination of anxiety, diet, lack of sufficient water,etc. Have an exam, drink water, eat healthy, seek counseling. Best!